I created a .ov2 file with 166 entries, but once uploaded to my GO LIVE 1005, the device claims that there are only 100 POI's in it (f.i. when I try to remove the Category). Is there a limit to the number of POIs one can define in one ov2 file? I searched the forums, but can't find any limit...

While there seems to remain a 100 category limit (it was raised to that number in Navcore 6 ages ago), no one I've heard has ever reported a limit to the individual POI count, and there are some folks with some astoundingly large lists out there. I used to think that one of my active categories that has 3300 points in it was big. You wouldn't believe what some other folks are running! I keep about 7000 custom points active at all times, plus what TomTom provides.